Gametogenesis in the Pacific Oyster Crassostrea gigas: A Microarrays-Based Analysis Identifies Sex and Stage Specific Genes

Background: The Pacific oyster Crassostrea gigas (Mollusca, Lophotrochozoa) is an alternative and irregular protandrous hermaphrodite: most individuals mature first as males and then change sex several times. Little is known about genetic and phenotypic basis of sex differentiation in oysters, and little more about the molecular pathways regulating reproduction. We have recently developed and validated a microarray containing 31,918 oligomers (Dheilly et al., 2011) representing the oyster transcriptome. The application of this microarray to the study of mollusk gametogenesis should provide a better understanding of the key factors involved in sex differentiation and the regulation of oyster reproduction. Methodology/Principal Findings: Gene expression was studied in gonads of oysters cultured over a yearly reproductive cycle. Principal component analysis and hierarchical clustering showed a significant divergence in gene expression patterns of males and females coinciding with the start of gonial mitosis. ANOVA analysis of the data revealed 2,482 genes differentially expressed during the course of males and/or females gametogenesis. The expression of 434 genes could be localized in either germ cells or somatic cells of the gonad by comparing the transcriptome of female gonads to the transcriptome of stripped oocytes and somatic tissues. Analysis of the annotated genes revealed conserved molecular mechanisms between mollusks and mammals: genes involved in chromatin condensation, DNA replication and repair, mitosis and meiosis regulation, transcription, translation and apoptosis were expressed in both male and female gonads. Most interestingly, early expressed male-specific genes included bindin and a dpy-30 homolog and female-specific genes included foxL2, nanos homolog 3, a pancreatic lipase related protein, cd63 and vitellogenin. Further functional analyses are now required in order to investigate their role in sex differentiation in oysters. Conclusions/Significance: This study allowed us to identify potential markers of early sex differentiation in the oyster C. gigas, an alternative hermaphrodite mollusk. We also provided new highly valuable information on genes specifically expressed by mature spermatozoids and mature oocytes

Ecological impacts of non-native Pacific oysters (Crassostrea gigas) and management measures for protected areas in Europe

Pacific oysters are now one of the most ‘globalised’ marine invertebrates. They dominate bivalve aquaculture production in many regions and wild populations are increasingly becoming established, with potential to displace native species and modify habitats and ecosystems. While some fishing communities may benefit from wild populations, there is now a tension between the continued production of Pacific oysters and risk to biodiversity, which is of particular concern within protected sites. The issue of the Pacific oyster therefore locates at the intersection between two policy areas: one concerning the conservation of protected habitats, the other relating to livelihoods and the socio-economics of coastal aquaculture and fishing communities. To help provide an informed basis for management decisions, we first summarise evidence for ecological impacts of wild Pacific oysters in representative coastal habitats. At local scales, it is clear that establishment of Pacific oysters can significantly alter diversity, community structure and ecosystem processes, with effects varying among habitats and locations and with the density of oysters. Less evidence is available to evaluate regional-scale impacts. A range of management measures have been applied to mitigate negative impacts of wild Pacific oysters and we develop recommendations which are consistent with the scientific evidence and believe compatible with multiple interests. We conclude that all stakeholders must engage in regional decision making to help minimise negative environmental impacts, and promote sustainable industry development

Gametogenic stages in triploid oysters Crassostrea gigas: Irregular locking of gonial proliferation and subsequent reproductive effort

International audienc

Identification of Ras, Pten and p70S6K homologs in the Pacific oyster Crassostrea gigas and diet control of insulin pathway

International audienc

Impact of energy storage strategies on gametogenesis and reproductive effort in diploid and triploid Pacific oysters Crassostrea gigas — Involvement of insulin signaling

International audienc

Adaptation to abiotic stress in the oyster Crassostrea angulata relays on genetic polymorphisms

Aquí describimos la resecuenciación completa del genoma de la ostra portuguesa Crassostrea angulata, una ostra ahuecada comestible de gran importancia comercial con un importante papel como biosensor de la contaminación de las aguas costeras. Secuenciamos el genoma de C. angulata con una cobertura de 29,3 veces utilizando el sistema ABI SOLID. Las comparaciones de las secuencias con el ensamblaje de referencia de la ostra del Pacífico (Crassostrea gigas) arrojaron 129 millones de SNP, 151.620 de los cuales se ubicaron en 20.908 genes de la base de datos de C. gigas. El análisis de los términos de ontología genética (GO) asociados con regiones genéticas que contienen SNP reveló que los términos GO significativos que mostraban diferencias entre las dos especies de ostras estaban relacionados con actividades de respuesta al estrés causado tanto por el secado como por la contaminación por metales. En el dominio del proceso biológico, los términos GO transporte de iones, fosforilación y procesos de proteólisis, entre otros, mostraron muchos genes polimórficos en C. angulata. Estos procesos están relacionados con la lucha contra el estrés genotóxico e hipoosmótico en la ostra. Es de destacar que más de 200 genes polimórficos se asociaron con procesos de reparación del ADN. Estos resultados revelan que la mayoría de los polimorfismos genéticos observados en C. angulata están asociados con procesos relacionados con la adaptación del genoma al estrés abiótico en regiones estuarinas y respaldan que los polimorfismos genéticos pueden ser la base de la capacidad observada de C. angulata para retener la extraordinariamente alta concentraciones de metales pesados tóxicos. Nuestros resultados también proporcionan el marco para futuras investigaciones para establecer las bases moleculares de la variación fenotípica de los rasgos adaptativos y deberían contribuir a la gestión de los recursos genéticos de la especie.Here we describe the whole genome re-sequencing of the Portuguese oyster Crassostrea angulata, an edible cupped oyster of major commercial importance with an important role as biosensor of coastal water pollution. We sequenced the genome of the C. angulata to 29.3-fold coverage using ABI SOLID system. Comparisons of the sequences with the reference assembly of the Pacific oyster (Crassostrea gigas), yielded 129 million SNPs, 151,620 from which were located in 20,908 genes from the C. gigas database. The analysis of Gene Ontology (GO) terms associated with gene regions containing SNPs, revealed that significant GO terms showing differences between the two oyster species, were related to activities of response to stress caused both by drying and by metal contamination. In the Biological Process domain, the GO terms ion transport, phosphorylation and proteolysis processes, among others, showed many polymorphic genes in C. angulata. These processes are related to combating genotoxic and hypo-osmotic stress in the oyster. It is noteworthy that more than 200 polymorphic genes were associated with DNA repair processes. These results reveal that most of the gene polymorphisms observed in C. angulata are associated with processes related to genome adaptation to abiotic stress in estuarine regions and support that genetic polymorphisms may be the base to the observed ability of C. angulata to retain the phenomenally high concentrations of toxic heavy metals. Our results also provide the framework for future investigations to establish the molecular basis of phenotypic variation of adaptive traits and should contribute to the management of the species' genetic resources.This study has been supported by the AQUAGENET project (SOE2/P1/E287), INTERREG IVB SUDOE program and by grants from the Junta de Andalucia (Spain) to the PAI BIO-219 group. The authors wish to thank to the Head of Bioinformatic Department in theGeneSystems Company, Juan Carlos Trivino, for his advice in the bioinformatic treatment of the data and Frederico Baptista from the IPMA (Portugal) for providing us the samples for the study